Book Image

Ceph: Designing and Implementing Scalable Storage Systems

By : Michael Hackett, Vikhyat Umrao, Karan Singh, Nick Fisk, Anthony D'Atri, Vaibhav Bhembre
Book Image

Ceph: Designing and Implementing Scalable Storage Systems

By: Michael Hackett, Vikhyat Umrao, Karan Singh, Nick Fisk, Anthony D'Atri, Vaibhav Bhembre

Overview of this book

This Learning Path takes you through the basics of Ceph all the way to gaining in-depth understanding of its advanced features. You’ll gather skills to plan, deploy, and manage your Ceph cluster. After an introduction to the Ceph architecture and its core projects, you’ll be able to set up a Ceph cluster and learn how to monitor its health, improve its performance, and troubleshoot any issues. By following the step-by-step approach of this Learning Path, you’ll learn how Ceph integrates with OpenStack, Glance, Manila, Swift, and Cinder. With knowledge of federated architecture and CephFS, you’ll use Calamari and VSM to monitor the Ceph environment. In the upcoming chapters, you’ll study the key areas of Ceph, including BlueStore, erasure coding, and cache tiering. More specifically, you’ll discover what they can do for your storage system. In the concluding chapters, you will develop applications that use Librados and distributed computations with shared object classes, and see how Ceph and its supporting infrastructure can be optimized. By the end of this Learning Path, you'll have the practical knowledge of operating Ceph in a production environment. This Learning Path includes content from the following Packt products: • Ceph Cookbook by Michael Hackett, Vikhyat Umrao and Karan Singh • Mastering Ceph by Nick Fisk • Learning Ceph, Second Edition by Anthony D'Atri, Vaibhav Bhembre and Karan Singh
Table of Contents (27 chapters)
Title Page
About Packt
Contributors
Preface
Index

How does erasure coding work in Ceph?


As with replication, Ceph has a concept of a primary OSD, which also exists when using erasure-coded pools. The primary OSD has the responsibility of communicating with the client, calculating the erasure shards, and sending them out to the remaining OSDs in the PG set. This is illustrated in the following diagram:

If an OSD in the set is down, the primary OSD can use the remaining data and erasure shards to reconstruct the data, before sending it back to the client. During read operations, the primary OSD requests all OSDs in the PG set to send their shards. The primary OSD uses data from the data shards to construct the requested data, and the erasure shards are discarded. There is a fast read option that can be enabled on erasure pools, which allows the primary OSD to reconstruct the data from erasure shards if they return quicker than data shards. This can help to lower average latency at the cost of a slightly higher CPU usage. The following diagram...